A light emitting device using a III-V nitride semiconductor, which can realize a blue-purple color and a blue-green color, has been applied to various fields such as flat panel displays, optical communication, etc.
Generally, the light emitting device using the III-V nitride semiconductor has a structure in which a nitride semiconductor is formed on a substrate. In the case of the light emitting device using the III-V nitride semiconductor, since the substrate and the nitride semiconductor have different lattice constants, if the nitride semiconductor is formed directly on the substrate, a defect concentration of the corresponding nitride semiconductor increases.
In order to solve the foregoing problem, a method for forming a buffer layer on a substrate prior to the stacking of a nitride semiconductor has been used to minimize defect generation during the succeeding nitride semiconductor formation. The process of forming the buffer layer will be described.
FIG. 1 is a sectional view explaining a conventional method for forming a buffer layer, and FIG. 2 is a photograph showing a surface of a substrate after the recrystallization during the formation of the conventional buffer layer.
The conventional buffer layer is formed by a process of forming low-temperature AlxGa1-xN(0≦x<1) on the substrate and recrystallizing the low-temperature AlxGa1-xN at ammonia (NH3) gas atmosphere. As illustrated in FIG. 1, the buffer layer composed of three-dimensional AlxGa1-xN(0≦x<1) seeds 102 in which the low-temperature AlxGa1-xN has been recrystallized is formed on the substrate 101 via the above process.
Meanwhile, when the recrystallized three-dimensional AlxGa1-xN seeds 102 are formed on the substrate 101, the corresponding recrystallized three-dimensional AlxGa1-xN seeds 102 are not uniformly distributed over the entire substrate 101. Therefore, after the recrystallization, the buffer layer, i.e., the three-dimensional AlxGa1-xN(0≦x<1) seeds 102 are formed in some areas of the substrate 101. Referring to FIG. 2, the three-dimensional AlxGa1-xN(0≦x<1) seeds are not formed over the entire substrate, and the substrate is exposed as it is in the areas other than the areas in which the three-dimensional AlxGa1-xN(0≦x<1) seeds have been formed.
In addition, the recrystallization of the low-temperature AlxGa1-xN is performed at NH3 gas atmosphere. The substrate in the areas in which the recrystallized three-dimensional AlxGa1-xN seeds do not exist is reacted with NH3 gas during the recrystallization. Normally, a sapphire (Al2O3) substrate is employed as the substrate. In this situation, the surface of the sapphire substrate is reacted with NH3 gas, and thus AlOyNz 103 is formed in some areas of the sapphire substrate as shown in FIG. 1.
The AlOyNz 103 formed in some areas of the substrate during the recrystallization has the lattice mismatch with a nitride semiconductor 104 formed via the succeeding process. Such lattice mismatch degrades the crystallinity of the nitride semiconductor 104.